In pictures: Russian military build-up near Ukraine

BBC: 10. April 2014

Russian soldiers prepare to fire their Msta-S self-propelled howitzer during military exercises in the southern Russia's Volgograd region, on April 2, 2014.

The decision of Nato's Supreme Headquarters in Europe (Shape) to release over 20 satellite images and associated maps of the Russian military build-up on Ukraine's eastern frontier is a signal of the concern among the Alliance's military commanders that a Russian military option against Ukraine is still very much on the table, the BBC's diplomatic correspondent Jonathan Marcus reports.

The imagery reportedly dates from late March and early April. It encompasses six locations in an arc around Ukraine's frontier.

The images show sophisticated warplanes, and helicopters an airborne early warning aircraft (similar to the Nato Airborne Early Warning and Control Aircraft, or Awacs)

a number of military deployments on the ground

Buturlinovka Air Base 

Satellite imagery of the formerly vacant Buturlinovka Air Base in Russia appears to show a Russian military build-up at three locations.

Yeysk Air Base

This satellite image reportedly from 2 April purports to show Russian Su-27/30 Flankers and Su-24 Fencers at the air base Yeysk

Among the most interesting of these is what is thought to be an airborne or Spetznaz (Special Forces) brigade at the Yeysk air base on the Sea of Azov some 20km (12 miles) from Ukrainian air space.

This satellite image reportedly from 22 March purports to show a Russian military airborne Special Forces brigade at Yeysk in southern Russia, near its border with Ukraine

This image reportedly taken on 22 March appears to show a Beriev A-50 Mainstay airborne early warning aircraft at Yeysk

At a number of other locations the massed vehicles of mechanised infantry or motor rifle brigades can be seen - not just tanks and infantry combat vehicles but artillery and the large number of supply trucks needed to keep a mechanised force on the move.

Belgorod

This satellite image reportedly from 26 March appears to show Russian Mil Mi-8 Hips and Mil Mi-24 Hinds near Belgorod, Russia

Tanks and IFV elements of Motorised Rifle Regiment are shown in this satellite image reportedly from 26 March near Belgorod

Novocherkassk

This satellite image reportedly from 27 March appears to show the marshalling of elements of a Motorised Rifle Regiment (MRR) near Novocherkassk, Russia

This image reportedly from 27 March appears to show a Russian artillery battalion at a military base near Novocherkassk, east of the Sea of Azov in southern Russia

Kuzminka

Russian military tanks and infantry fighting vehicles appear to be shown in this satellite image reportedly from 27 March of a military base near Kuzminka, southern Russia

This satellite image from 27 March appears to show tanks and supply elements of a brigade near Kuzminka, close to Ukraine's eastern border

Russia has responded to the release of the images by saying that the satellite photos were actually taken in 2013.

A Nato spokesman says that they have not altered the images in any way and that the dates indicated on the slides were placed there by DigitalGlobe. There was no immediate comment from DigitalGlobe, when approached by BBC News.